The range equation in ultrasound is used to determine which of the following?

• A. Reflector depth
• B. Reflector amplitude
• C. Reflector frequency
• D. Reflector direction

Answer: (A)

The range equation is about converting the time it takes for a sound pulse to travel to a reflector and back into a depth estimate. Since the pulse must go out and return, the depth is half the product of the speed of sound in tissue and the round-trip time: depth = (speed × time) / 2. In soft tissue, the speed is about 1540 m/s, but the exact value is used as a constant in the calculation. This is why the range equation determines reflector depth.

Amplitude, frequency, and direction aren’t derived from this equation. Amplitude relates to how strongly the interface reflects energy and to attenuation, frequency depends on the transducer and tissue effects, and direction comes from the imaging geometry and steering. The key idea is that time-of-flight with a known speed of sound gives depth.